In her report, Wright referred to work by the British Royal Society which found the environmental risks associated with fracking could be managed effectively, provided operational best practices were implemented and enforced through regulation.

"But at this stage I cannot be confident that operational best practices are actually being implemented and enforced in this country," Wright said in her report.

One issue was that companies were perhaps being trusted rather too much to all do the right thing.

The second stage of her investigation would look at how well the environmental risks associated with fracking were being regulated and monitored.

While discussing the interim report, Wright warned that if she found issues that were sufficiently worrying she would not hesitate to call for a moratorium.

The report raised concerns about whether New Zealand would be able to cope with a surge in fracking activity.

"If, for instance, exploration drilling on the east coast of the North Island reveals the presence of commercial quantities of oil that can be recovered through fracking, an 'oil rush' would likely follow - many exploration wells could be drilled in a very short time with production not far behind."

Such rapid scaling up had led to well-publicised problems in other countries.

"The scale and speed of change that could occur requires forethought now. We need to prepare for a future that might take us by surprise," Wright said in the report overview.

The potential for important aquifers to be contaminated as a result of fracking was "very real". While there was much concern about the chemicals in fracking fluid, the salty water that came from deep under the ground along with the oil and gas was much greater in volume, and could also contaminate groundwater.

Internationally, there were many anecdotal examples of aquifer contamination after nearby wells had been fracked.

Spills and leaks were one way fracking could lead to water contamination, but were relatively easy to manage.

Another way was through migration, where oil and gas or other fluids travelled up through cracks in the rock and eventually reached aquifers.

The possibility of contaminants migrating into aquifers through cracks created during the fracking process was only a remote possibility because the cracks were unlikely to be long enough to create pathways in the rock between the fracking zone and aquifers, the report said.

It was possible cracks produced by fracking could connect to natural fractures or faults in the ground, and create a pathway, the report said.

But it also said: "While possible, the probability of fracking fluids migrating to freshwater aquifers or the surface is very unlikely."

The third possible way fracking could lead to water contamination was through well failure.

"To date, there is no evidence that fracking has caused groundwater contamination in New Zealand, and at the current scale of operations, the risk appears low," the report said.

Another major concern was the potential for triggering earthquakes. The process of fracking itself caused only "very tiny" earthquakes.

"But if liquids (fracking fluid or wastewater) were to find their way into an already stressed fault, the fault might slip triggering a more significant (though probably small) earthquake," the report said.

There were three documented overseas cases where fracking fluid injection had reached nearby active faults and caused earthquakes. Those earthquakes were all less than magnitude-4 and caused no surface damage or water contamination from well damage.

The first known use of fracking in this country was in 1989, with almost all the fracking in New Zealand taking place in Taranaki.